1. Field of the Invention
The present invention relates in general to transducers, and more particularly to acoustic transducers and transducer arrays. The present invention also relates to a transducer capable of radiating steered directional acoustic energy from a single transducer.
2. Background and Discussion
Traditionally arrays of sonar transducer are used to form directional beams that can be electronically steered to various directions. They often take the form of planar, spherical or cylindrical arrays. U.S. Pat. No. 3,290,646, xe2x80x9cSonar Transducer,xe2x80x9d by S. L. Ehrlich and P. D. Frelich describes an invention where beams are formed and steered from one transducer in the form of a cylinder. Cardioid beam patterns are formed through the combination of extensional monopole and dipole modes of vibration of a piezoelectric tube, cylinder or ring. Ehrlich has also described a spherical type transducer device in U.S. Pat. No. 3,732,535. The cardioid beam pattern function yields beam widths that are rather broad with a value of approximately 131xc2x0, limiting the degree of localization.
It is the general object of the present invention to provide a transduction apparatus, which employs multiple modes to obtain an improved more directional steered beam pattern.
Another object of the present invention is to provide a transduction apparatus, which employs multiple modes including the quadrupole mode to obtain an improved, more directional, steered beam pattern.
Still another object of the present patent is to provide a constant beam pattern and smooth response over a broadband operating range.
A further object of the invention is to provide a simply excited beam with operation in the range between the dipole and quadrupole modes.
To accomplish the foregoing and other objects, features and advantages of the invention there is provided an improved electromechanical transduction apparatus that employs a means for utilizing the electromechanical transducer in a way so that higher order modes of vibration are excited in a controlled prescribed manner so as to yield a directional beam pattern.
In accordance with the invention there is provided an electromechanical transduction apparatus that is comprised of a continuous piezoelectric shell or tube with electrodes arranged to excite modes of vibration which can be combined to obtain an improved directional pattern. The combination can result from a specification of the voltages on the electrodes and can yield a uniform broadband response.
The transducer system may be of piezoelectric, electrostrictive, single crystal or magnetostrictive material operated in the 33 or 31 drive modes and typically takes the form of a ring, cylinder or spherical shell operating in extensional modes of vibration. However, inextensional modes of vibration, such as bender shell modes, may also be used to achieve directional patterns and allow a more compact lower frequency transducer system.
In one embodiment of the invention a piezoelectric cylinder is driven into its first three extensional modes by means of eight electrode surfaces. In another embodiment the modes are excited by sixteen groups of piezoelectric bars, which together constitute the ring or cylinder.
As a reciprocal device the transducer may be used as a transmitter or a receiver and may be used in a fluid, such as water, or in a gas, such as air.